1 00:00:13,460 --> 00:00:21,140 So we've been told once again that rather one is not able to ping the loopback of router four and that's 2 00:00:21,140 --> 00:00:22,640 what we're seeing in the lab. 3 00:00:23,180 --> 00:00:30,800 So on router one show IP route, we don't have a route to network four in the routing table, but we 4 00:00:30,820 --> 00:00:33,530 are learning routes through OSPF. 5 00:00:34,040 --> 00:00:42,380 So as an example, we can ping the loopback of router to show OSPF neighbor shows us that we have a 6 00:00:42,770 --> 00:00:45,770 OSPF relationship to router two. 7 00:00:49,380 --> 00:00:50,100 And rather to. 8 00:00:50,100 --> 00:00:55,290 We can confirm that rather too has this IP address configured. 9 00:00:56,090 --> 00:01:01,220 On loopback is zero and that's the IP address. 10 00:01:01,280 --> 00:01:10,940 That router one can ping, but rather one doesn't see network four in its routing table and neither 11 00:01:10,940 --> 00:01:17,330 does router to write a two is learning about the loopback of right one. 12 00:01:17,810 --> 00:01:24,050 So router two can ping the loopback of router one, but it doesn't look like it's learning about the 13 00:01:24,050 --> 00:01:31,400 loopback of router three, which is 3.3.3.3. 14 00:01:32,420 --> 00:01:36,740 And it's also not a learning about the loopback of router four. 15 00:01:37,580 --> 00:01:44,420 So show IP protocols once again shows us that we running OSPF with process ID one. 16 00:01:44,750 --> 00:01:51,710 We have two normal areas configured, so a number of areas in this routers two. 17 00:01:51,920 --> 00:01:56,840 There are two normal areas, zero stub and zero not so stubby areas. 18 00:01:57,230 --> 00:02:02,990 The router knows about rather one and itself again on router one. 19 00:02:04,010 --> 00:02:05,000 The loopback. 20 00:02:05,770 --> 00:02:07,600 He's configured as follows. 21 00:02:09,550 --> 00:02:15,610 But the Rada doesn't know about Rada three or out of four. 22 00:02:16,060 --> 00:02:19,600 Is OSPF enabled on this interface? 23 00:02:20,110 --> 00:02:28,270 So show IP OSPF interface OSPF is enabled on the loopback interface of the router. 24 00:02:28,780 --> 00:02:31,600 It's enabled on gigabit 001. 25 00:02:32,320 --> 00:02:40,960 In other words, it is enabled on this interface and it's also enabled on gigabit 000. 26 00:02:41,740 --> 00:02:46,630 So OSPF is configured on this interface. 27 00:02:47,780 --> 00:02:50,390 Can we ping root of three? 28 00:02:51,410 --> 00:02:52,550 Yes, we can. 29 00:02:52,730 --> 00:02:59,630 So we have IP connectivity to router three, but we don't have an OSPF relationship to router three. 30 00:03:00,440 --> 00:03:06,320 Even though OSPF is enabled on this network. 31 00:03:06,770 --> 00:03:11,510 So let's have a look at router three and see if there's a problem on router three. 32 00:03:12,440 --> 00:03:14,990 He has brought a three show IP protocols. 33 00:03:15,290 --> 00:03:18,320 OSPF is enabled on this router. 34 00:03:18,910 --> 00:03:21,890 Number of areas configured on the shroud is one. 35 00:03:22,790 --> 00:03:25,850 There's one normal area configured on the Cerrado. 36 00:03:27,200 --> 00:03:29,630 So IP OSPF interface. 37 00:03:30,020 --> 00:03:36,440 So let's have a look at this output and compare it to the output on rather two. 38 00:03:37,220 --> 00:03:39,890 Can you see a problem here? 39 00:03:40,810 --> 00:03:43,990 Based on this output, you should be able to see a problem. 40 00:03:44,260 --> 00:03:46,030 What's the problem here? 41 00:03:46,880 --> 00:03:49,700 Pause the video if you need to at this point. 42 00:03:51,080 --> 00:03:51,410 Okay. 43 00:03:51,410 --> 00:04:00,770 So have a look at the output on gigabit or zero one, which is this interface versus gigabit 001, the 44 00:04:00,770 --> 00:04:02,660 output on this interface. 45 00:04:03,890 --> 00:04:11,870 Notice the area configured on 10.1 or 2.1 is area zero. 46 00:04:12,290 --> 00:04:20,420 Whereas on this site it's area two, OSPF requires that neighboring routers be in the same area. 47 00:04:20,570 --> 00:04:29,330 So show run shows us that this interface has been configured in area two. 48 00:04:30,050 --> 00:04:35,900 This interface needs to be configured in Area zero to match router two. 49 00:04:36,170 --> 00:04:43,250 It's a requirement in OSPF that all areas be connected to area zero. 50 00:04:43,670 --> 00:04:47,570 The area configured on this side is area one. 51 00:04:47,570 --> 00:04:57,890 So router two is an area border router or ABR with this interface in area zero and this interface in 52 00:04:57,890 --> 00:04:59,060 Area one. 53 00:04:59,360 --> 00:05:07,040 That means that router three should have this interface gigabit or zero zero configured in another area 54 00:05:07,040 --> 00:05:08,630 such as area two. 55 00:05:08,840 --> 00:05:14,180 But this interface should be configured in area zero. 56 00:05:14,420 --> 00:05:25,040 So conf t interface gigabit zero one ip ospf one, area zero show run. 57 00:05:26,690 --> 00:05:29,600 That interface is now configured in area zero. 58 00:05:29,960 --> 00:05:32,270 And notice what we see on the side. 59 00:05:32,480 --> 00:05:39,770 Router two has formed a neighbor relationship to router three on gigabit 001. 60 00:05:40,430 --> 00:05:43,370 On this side, however, we don't see any output. 61 00:05:43,700 --> 00:05:53,840 Show IP OSPF neighbor shows us that we have two full relationships one to router two and one to write 62 00:05:53,840 --> 00:05:54,620 a four. 63 00:05:54,770 --> 00:05:56,570 So that looks good. 64 00:05:56,570 --> 00:06:00,740 But why are we not seeing output on the screen? 65 00:06:01,590 --> 00:06:02,910 And here's your answer. 66 00:06:03,240 --> 00:06:07,230 We want to enable logging to the console. 67 00:06:07,620 --> 00:06:09,990 Be careful in the exam. 68 00:06:09,990 --> 00:06:11,820 You may not be able to do that. 69 00:06:12,650 --> 00:06:19,160 But logging to the console will show us when a neighbor relationship goes down and when it comes up 70 00:06:19,160 --> 00:06:19,820 again. 71 00:06:20,330 --> 00:06:29,510 So as an example, notice here we can see that the router has been configured from the console by the 72 00:06:29,510 --> 00:06:30,230 console. 73 00:06:30,260 --> 00:06:37,850 Again, Control Z or Control Z shows us that when logging is disabled, you won't see that output and 74 00:06:37,850 --> 00:06:41,090 you won't see messages on the screen such as this. 75 00:06:41,330 --> 00:06:43,940 So make sure that logging is enabled. 76 00:06:44,720 --> 00:06:45,050 Okay. 77 00:06:45,050 --> 00:06:48,380 So can router three ping the loopback of router four? 78 00:06:49,360 --> 00:06:50,960 Looks like it can't. 79 00:06:50,960 --> 00:06:55,790 So we need to check what the problem is on the side of the network. 80 00:06:56,420 --> 00:06:57,800 Show IP route. 81 00:06:57,920 --> 00:07:02,690 Router three is learning rots and can ping the loopback of rotor. 82 00:07:02,690 --> 00:07:10,340 One is an example and keeping the loopback of router two but can't ping the loopback of router four. 83 00:07:10,670 --> 00:07:13,850 Can it ping a router for? 84 00:07:13,880 --> 00:07:18,050 Yes, it can show ip ospf interface. 85 00:07:18,980 --> 00:07:25,340 Thus interface gigabit is zero zero is enabled in OSPF in area two. 86 00:07:26,270 --> 00:07:32,030 The loopback is enabled in area two and gigabit is zero one. 87 00:07:32,690 --> 00:07:34,280 So that looks good. 88 00:07:34,370 --> 00:07:36,770 Let's check what's happening on right for.